Coral estimates the value of Three-fourths times 9.3. Which estimate is reasonable? 6 9 12 16

How do i simply this expression (quadratic formula basis) on a ti-84 or normal calculator?

Pls brainliest will be awarded if answer is correct

I'm at a bookstore with $\$35$ in my pocket and a $20\%$-off coupon. what is the cost of the most expensive book i can buy with my money and the coupon? (assume that there are books of every possible price in the bookstore. it's a large bookstore! )